L1-protein in incipient lymphocyte-depleted graft-versus-host disease. Expression in keratinocytes and coexpression with Factor XIIIa in dermal cells

With the introduction of effective immunosuppressive regimens some cutaneous rashes following bone marrow transplant may appear histologically unremarkable. We report three cases of cyclosporin-abated cutaneous graft-versus-host reaction (GVHR) where the most straightful histologic clue was the epidermal L1-protein (calprotectin) expression revealed by a positive immunolabelling using the Mac 387 antibody. The epidermis looked otherwise normal and inflammatory cells were scant in the dermis. The expression of calprotectin by keratinocytes occurred early in cutaneous GVHR. In addition, CD45RO-positive T memory lymphocytes were exceedingly rare in the dermis while a few Mac 387-positive monocytes coexpressed Factor XIIIa immunoreactivity. Hyperplasia of the Factor XIIIa-positive dendrocytic population was obvious. Calprotectin and Factor XIIIa immunolagellings should be regarded as a diagnostic adjunct in lymphocyte-depleted cutaneous GVHR. Calprotectin positivity of the epidermis is indicative although not specific for such condition. However, its combination with a low lymphocytes/monocytes ratio in the dermis which is enriched in plup dendrocytes is almost diagnostic.